Method of treating rubber and product obtained thereby



Patented Oct. 17, 1944 UNITED {STATES PATENT orncs METHOD OF TREATINGRUBBER AND PRODUCT OBTAINED THEREBY Robert L. Sibley, Nitro, W. Va.,assignor to Monsanto Chemical Company, St. Louis, Mo., a corporation ofDelaware No Drawing. Application January 9', 1942, Serial No. 426,240

19 Claims.

The present invention relates to a method of improving the physicalproperties of rubber and to the vulcanizates obtained by heating rubberand sulfur in the presence of a new class of treating agents.

In accordance with the present invention it has been discovered thatchlor substituted diphenyls retard cracking and checking of rubberarticles. It is well known that prolonged flexing of. a rubber compoundas is encountered for example durl0 2,291,988, of which the presentapplication is a continuation-in-part.

While more than one chlorine substituent may be present on the diphenylnucleus, the mono chlor substituted diphenyls have been found to beparticularly efiective.

As specific embodiments of the invention to illustrate the same butwithout limiting the invention, rubber stocks were compoundedcomprising:

Smoked sheets rubber bl k Mercaptobeuzothiazole Condensation product ofp-amino diphenylacetone p-Chlor diphenyl Mineral acid rearranged2,2,4-trimethyl dihydroquinoline Parts Parts Parts Parts Pgrts PartsParts Parts by by by weight weight weight weight weight weight weightweight 100 100 1 1 l 100 1 100 mg the natural wear of a rubber tire,results in a checking and cracking of the rubber which seriouslyshortens the life and usefulness of the article. The phenomenon ofchecking apparently is independent of antioxidant activity. In any eventthe strength of a rubber antioxidant is no criteria of the resistance toflex-cracking imparted to the rubber. Since the antioxidant propertiesof the chlor diphenyls, if any, are weak, it is preferred to use them inconjunction with the common rubber antioxidants. Surprisingly smallamounts are effective. As little as 0.05 part by Weight on 100 parts byweight of the rubber exert an appreciable affect but it is preferred touse 0.10 part by weight on the rubber in order to provide an adequatemargin of safety. Up to 0.2 part have been employed with somewhatincreased eflects as the amount is increased. While even higher amountscan be used where desired, there is no further improvement in theflex-cracking resistance. Since the chlor substituted diphenyls are oflimited solubility in rubber, the amount incorporated into the rubbermust be kept low where a bloom is undesirable. However, where a bloomcan be permitted, it is highly advantageous to increase the amount, sayup to 3.0 parts by weight, so as to produce on the surface of the rubbera thin flexible uniform layer of chlorinated diphenyl. In this mannerthe resistance of the rubber to sunchecking can be materially enhanced.The use of chlorinated diphenyls to prevent the checking and cracking ofrubber upon exposure to sunlight is disclosed in co-pending application,Serial No. 212,773 filed June 9, 1938, now U. S. Patent No.

The stocks so compounded were vulcanized in the usual manner by heatingfor different periods of timein a press at the temperature of 30 poundsof steam pressure per square inch and then artificially aged by heatingin an oven at 70 C. for fourteen days. The flex cracking resistance ofthe vulcanized products was determined, both before and after aging, bymeans of a flexing ma,- chine as set forth by L. V. Cooper, AnalyticalEdition of Industrial and Engineering Chemistry, vol. 2, No. 4, 1930,pages 391-394. Since the actual number of flexings before failure of agood rubber stock is of the order of several hundred thousand flexes, itis convenient to refer to an arbitrary scale for purposes of relativeevaluation. Accordingly, the results are based upon the number 30 for acontrol stock. While the control stock is not shown it is simply arubber stock similar to those set forth above containing a standardantioxidant. On this arbitrary scale a difference of one represents adifference of approximately 10,000 fiexings. Thus, the figures in thetable below are not based opon any particular number of flexings but thedifferences in the figures do represent diiferences in the actual numberof flexings. Furthermore, the unaged flexing results are based on anunaged control stock and the aged flexing results are based on an agedcontrol stock. Therefore, the aged and unaged results are independent ofeach other. In other words a higher figure after aging does notnecessarily represent a higher number of flexes after aging butindicates that the stock flexed rela- 0 tively better after aging thandid the control stock and therefore showed less deterioration in thisrespect. .Each stock was flexed until visible cracking and checkingappeared. The flexing figures therefore show the differences in thenumber of flexings between the control stock and the the flex crackingresistance. As further specific embodiments of the inventionillustrating this application of the new materials, but again withoutlimiting the invention, rubber stocks were compounded comprising Stock JK L M N Pa rte Parts Parts Parts Parts Parts by by by by by weightweight weight weight weight weight Smoked sheets. rubber 100 100 100 100100 100 50 50 50 50 O 50 5 5 5 5 5 5 3 3 3 3 3 3 .2 2 2 ,2 2 2 Stearic a3 3 3 3 3 3 Mercaptobenzothiazole 0.75 0.75 0.75 0.75 0. 75 0. 75Mineral acid rearranged 2,2,4-

trimethyl dihydroquinoline 1.0 0.9 p-Chlor diphenyl 0.1 0.1 0. l5Condensation product of p-amino diphenyl-acetone 1.0 0. 9 l. 5 l. 35

test stocks after all stocks have deteriorated to the same extent.

Flexlng, figure Stock Aged 14 days as 0.05 part "by weight of p-chlordiphenyl to a rubber stock increases the .number of flexes beforefailure by approximately 10,000. amounts result in even furtherimprovement. The addition of 0.1 part by weight of p-chlor di- Dhenylincreased the number .of .fiexes in every case, .both before and after.aging, by approximately, 20,000 flexes.

In order to determine ,the age resistance of the stocks so compounded,they were aged in abomb at 225 and under .50 pounds air pressure persquare inch. The modulus and tensile properties of .the aged and unaged.rubber products are set forth below:

Table ,I

Modulus of elasticity in Cure Hrs lbs/in. at Tensile at. Ult. Stock timein 8 d elongations ofbreak in elong,

mins. g lbs/in 9 percent 160' 0 1, 125 3,000 4,260 555 60 I 1,525 3, 2703, 640 470 00 0 1,080 3,050 4, 300 560 60 15 1, 505 3, .210 3, 855 49060 0 r 1, 110 v2, 980 4, 360 .570 60 15 1,485 3, 300 3, 810 470 60 0 1,=140 2,960 4,300 530 60 15 1, 455 3, 275 3, 715 465 60 0 1, 135 3,040 4,350 540 60 15, 1,515 3, 320 13, 550 430 60 0 l, 160 3, 080. 4, 250 .53060 15 1,435 3, 280 3, 280 400 60 0 1, 160 3,120 4, 540 550 60 15 1, 5053, 420 3, 420 400 60 0 1, 150 3, 100 4, 620 540 60 15 1,420 3,325 3, 440410 The above data show the desirable aging properties of rubber stockscontaining, thepreferred class of materials.

The preferred class of materials can be used to :replace part of theantioxidant normally used in a rubber composition without sacrificingthe age resistance and at the same time improving Higher The stocks socompounded were vulcanized by heating for different periods of time in apress at the temperature of thirty pounds of steam pressure per squareinch and artificially aged by heating in an oven at 70 C. for sevendays. The resistance to flexing was then determined as described above.

Flexlng figure Stock Un- Aged aged 7 days Representative stocks wereartificially aged in a bomb at 225 C. and under .50 pounds air pressureper square inch.

Table II Modulus of C l ii t r '1 t ure 5. in. a ensr e a Stock time in2 35 ,elongations ofbreak in g" minutes g lbs/in. 3

These results show replacement of part of the antioxidant by thepreferred class of materials has provided rubber compositions ofexcellent resistance to aging.

Obviously practice of this invention is not limited to thespecificcompositions given above. The preferred class of materials may beemployed in different proportions than herein described and inconjunction with other rubber compositions than those specificallydisclosed, for this invention is applicable generally to pure rubber orrubber compositions of the most varied nature. The amount of treatingagent, however, is always small with respect to the rubber. That is tosay "the amount is insuflicient to alter or diminish the rubberyproperties, particularly the elasticity and modulus and tensilestrength.

It is to be understood that the term treating as employed in theappended claims is used in a generic sense to include either theincorporating of the preferred class of materials into the rubber bymilling or similar process, or their addition to the rubber latex beforeits coagulation, or the application thereof to the surface of a mass ofcrude or vulcanized rubber. The term a rubber is employed in the claimsto define a vulcanizable plastic material which possesses highextensibility under load coupled with the property of forciblyretracting to approximately its original size and shape after the loadis removed. Such products include, for example, india rubber, reclaimedrubber, balata, gutta percha and other natural or synthetic vulcanizableproducts which deteriorate upon aging whether or not admixed withfillers, pigments or accelerating agents.

The present invention is limited solely by the claims attached hereto aspart of the present specification.

What is claimed is:

1. The method of improving the physical properties of a rubber whichcomprises treating a rubber with a chlor diphenyl unsubstituted exceptfor chlorine in an. amount not exceeding 0.2 percent by weight on therubber.

2. The method of improving the physical properties of a rubber whichcomprises treating a rubber with mono chlor diphenyl unsubstitutedexcept for chlorine in an amount not exceeding 0.2 percent by weight onthe rubber.

3. The method of improving the physical properties of a rubber whichcomprises treating a rubber with p-chlor diphenyl in an amount notexceeding 0.2 percent by weight on the rubber.

4. The method of improving the phyhical properties of natural rubberwhich comprises treating natural rubber with a mono chlor diphenylunsubstituted except for chlorine in an amount not exceeding 0.2 percentby weight on the rubber.

5. The method of improving the physical properties of natural rubberwhich comprises treating natural rubber with p-chlor diphenyl in anamount not exceeding 0.2 percent by weight on the rubber.

6. The method of improving the physical properties of natural rubberwhich comprises treating natural rubber with a conventional antioxidantin conjunction with p-chlor diphenyl in an amount not exceeding 0.2percent by weight on the rubber.

7. The method of improving the physical properties of natural rubberwhich comprises treating natural rubber with a ketone-amine typeantioxidant in conjunction with p-chlor diphenyl in an amount notexceeding 0.2 percent by weight on the rubber.

8. The method of improving the physical properties of natural rubberwhich comprises treating natural rubber with mineral acid rearranged2,2,4-trimethyl dihydroquinoline in conjunction with about 0.1 percentby weight on the rubber of p-chlor diphenyl.

9. The method of improving the physical properties of natural rubberwhich comprises treating natural rubber with the condensation product ofacetone and p-amino diphenyl in conjunction with about 0.1 percent byweight on the rubber of p-chlor diphenyl.

10. The vulcanized rubber product obtained by heating a rubber andsulfur in the presence of a chlor diphenyl unsubstituted except forchlorine in an amount not exceeding 0.2 percent by weight on the rubber.

11. The vulcanized rubber product obtained by heating a rubber andsulfur in the presence of mono chlor diphenyl unsubstituted except forchlorine in an amount not exceeding 0.2 percent by weight on the rubber.

12. The vulcanized rubber product obtained .by heating a rubber andsulfur in the presence of p-chlor diphenyl in an amount not exceeding0.2 percent by weight on the rubber.

13. The vulcanized rubber product obtained by heating natural rubber andsulfur in the presence of a mono chlor diphenyl unsubstituted except forchlorine in an amount not exceeding 0.2 percent by weight on the rubber.

14. The vulcanized rubber product obtained by heating natural rubberandsulfur in the presence of p-chlor diphenyl in an amount not exceeding0.2 percent by weight on the rubber.

15. The vulcanized rubber product obtained by heating natural rubber andsulfur in the presence of a conventional rubber antioxidant inconjunction with p-chlor diphenyl in an amount not exceeding 0.2 percentby weight on the rubber.

16. The vulcanized rubber product obtained by heating natural rubber andsulfur in the preseice of a ketone-amine type antioxidant in conjunctionwith p-chlor diphenyl in an amount not exceeding 0.2 percent by weighton the rubber.

17. The vulcanized rubber product obtained by heating natural rubber andsulfur in the presence of mercaptobenzothiazole and a ketoneamine typeantioxidant in conjunction with p-chlor diphenyl in an amount notexceeding 0.2 percent by weight on the rubber.

18. The vulcanized rubber product obtained by heating natural rubber andsulfur in the presence of mineral acid rearranged 2,2,4-trimethyldihydroquinoline in conjunction with about 0.1 percent by weight of therubber of p-chlor diphenyl.

19. The vulcanized rubber product obtained by heating natural rubber andsulfur in the presence of the condensation product of acetone andp-amino diphenyl in conjunction with about 0.1 percent by weight on therubber of p-chlor diphenyl.

ROBERT L. SIBLEY.

